It is known in the automotive technology that, for the increase of the ratio spread in a shift transmission, a non-synchronized transfer gear box is connected downstream. The transfer gear box can be, for instance, designed in two steps with a speed increase step as a road gear and a speed reduction step as an off road gear.
For instance, known through the publication WO 2010/006872 A1 is a method to control a drive train of a vehicle with a drive motor and a main transmission, and with a transfer gear box, through which shifting is automatically executed in the transfer gear box during the drive. Hereby, the drive train is separated from the powershift transmission, the transfer gear box is shifted and a suitable gear will be engaged again in the powershift transmission. This situation necessarily causes an interrupt of the traction force because for shifting to the speed increasing step or to the speed reduction step in the transfer gear box, it necessarily requires an interrupt of the traction force.